Predatory hymenopteran assemblages in boreal Alaska: associations with forest composition and post-fire succession

Changes to the fire regime in boreal Alaska are shifting the ratio of coniferous to deciduous dominance on the landscape. The increase in aspen and birch may have important effects on predatory hymenopteran assemblages by providing a source of extrafloral nectar and increasing prey availability. Furthermore, fire-induced changes in successional age alter habitat structure and microclimate in ways that may favor ants. This study is the first to characterize the influence of fire-related vegetation changes on boreal predatory hymenopteran assemblages. We compare the abundance, species richness, and composition of predatory hymenopteran assemblages among forests at different stages of succession and of varying post-fire tree species compositions. Ant assemblages were weakly related to forest composition, but ants were significantly more abundant and speciose in early-successional forests than in mid-late successional forests. In contrast, macropterous wasp morphospecies richness and abundance, and micropterous wasp abundance, were positively related to the basal area of aspen, but were not related to successional stage. The results suggest that shifts in boreal vegetation related to climate warming will result in changes to the predaceous insect community, with ants responding positively to disturbance and wasps responding positively to an increase in the representation of aspen on the landscape.

阿拉斯加寒带地区的火灾制度（fire regime）变化正在改变景观中针叶树与落叶树的优势占比。山杨与桦树种群的扩张，可通过提供花外蜜源并提升猎物可获得性，对捕食性膜翅目昆虫（predatory hymenopteran）类群产生重要调控作用。此外，火灾诱导的演替年龄变化会改变栖息地结构与微气候，进而可能对蚁类群落产生有利影响。本研究首次阐明了火灾相关植被变化对寒带捕食性膜翅目昆虫类群的影响。我们对比了不同演替阶段、不同火烧后树木物种组成的森林中，捕食性膜翅目昆虫类群的多度、物种丰富度与群落组成。结果显示，蚁类群落与森林组成的相关性较弱，但早期演替森林中的蚂蚁多度与物种丰富度均显著高于中晚期演替森林。与之相反，长翅型（macropterous）蜂类形态种（morphospecies）的丰富度与多度，以及短翅型（micropterous）蜂类的多度，均与山杨的胸高断面积（basal area）呈正相关，但与演替阶段无关。研究结果表明，与气候变暖相关的寒带植被变化将引发捕食性昆虫群落的结构改变：蚂蚁对干扰产生正向响应，而蜂类则随景观中山杨占比的提升呈现正向响应。